Real-time monitoring of immunoglobulin G levels in milk using an ordered porous layer interferometric optical sensor.

Immunoglobulin G (IgG) is a significant ingredient of immunological activity in milk and colostrum, the activity and content of which is easily disturbed by potentially conditional variant during sterilization. Therefore, developing robust methods for the detection of IgG levels in milk is especially important. Herein, protein A from the Staphylococcus aureus functionalized silica colloidal crystalline film (SCC@SPA) sensing unit combined with ordered porous layer interferometry (OPLI) for IgG detection in untreated bovine milk was developed. Calibration curves in milk and buffer were set up by the variations of the optical thickness (OT) of the sensing unit after the IgG association and dissociation phases. The influence of temperature on the level of IgG was evaluated. Furthermore, the identification of IgG levels with pasteurized milk and ultrahigh temperature (UHT) sterilized milk from the market randomly was successfully carried out without any sample pretreatment. More importantly, compared with other methods, this novel method has the advantages of convenient operation, low cost, and suitability for point-of-care (POC) testing.